Polyvinyl acetate emulsion containing an acetic acid ester of glycerol



Patented Feb. 17, 1953 U i T D STA?? are reics.

POLYVINYL ACETATE EMULSION CONTAIN ING AN ACETIC ACID ESTER. OF GLYCEROL.

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No Drawing, Application April 6, 1950', Serial No. 154,429

4 Claims.

This invention relates to emulsions of polymers which are suitable for use as coatings and as adhesives. It is particularly concerned with such an emulsion of polymers which is capable of providing a water-resistant bond or coating and which at the same time retains the stability, fluidity and the various other physical properties of such an emulsion which make it particularly useful as acoating or adhesive.

The use of melts and solutions of water-insolublev artificial resins in the coating and adhesive art has been supplanted to a large extent by emulsions of such resins, particularly polyvinyl acetate emulsions, due to the improved ease, econom and safety with which aqueous emulsions of the resin may be employed. On the other hand, the usefulness of water-insoluble polymer emulsions has been limited by the characteristic lack of water-resistance of the coatings and bonds deposited therefrom at room temperature and the tendency'of such coatings and bonds to re-emulsify or disintegrate when subsequently brought into contact with water during the course of normal use of the object or article to which they have been applied.

This lack of water-resistance has been considered innate in the coatings and films deposited from such polymer emulsions inasmuch as watersoluble emulsifying and bodying agents are employed necessarily to establish and stabilize the emulsion. These agents are apparently carriedv into the film or bond deposited from the emulsion upon application of the emulsion to a surface, and actively exhibit the emulsifying eiiect on the polymer comprising the body of the coating or film and cause its redispersion when the surface is brought into contact with water.

Various proposals have been made to obviate the water-sensitivity of the coatings or bonds deposited from such emulsions, but in general these proposals have been directed to modifying emulsions of such polymers "which have been prepared in a specific manner, or require treating the emulsion with certain diluents immediately prior to its application due to the recognized tendenc of the suggested diluents to either break or gel the emulsion shortly after the addition of the diluent.

Prior to the instant invention, forexample a common expedient for increasing the water-resistance of a coating or film; deposited from a water-insoluble polymer emulsion included the addition of a quantity of one or more substances such as dimethylol urea, trimethylol melamine, certain chromium salts, strong acids or highly reactive aldehydes such as glyoxal, certain resins,

mer emulsion immediately prior to use as the reu s o ons, we e. un t e and er ain. of the substances resulted in a progressive increase in theviscosity of the emulsion until a gel was formed. Gelling rendered the composition completely unfit for use in adhesive applicator machines operated at high, speed. Additionally, the modification affected by some of' these substances did not result in a substantial improvement in the water-resistance of the coating or film deposited from the emulsion, and often imparted undesirable color and foaming character istics to the emulsion.

Where thermoplastic polymeric material has been employed, it has been suggested that the water-resistance of the coating or bond deposited from an emulsion of the material can be improved by heating the coating or bond sufiiciently to cause coalescence of the material into a homogeneous mass. suitable Where the emulsion is employed as a quick-setting adhesive in high-speed mechanical applicators, and in any event the drying and heating suggested is often impractical.

A further suggestion directed to retaining the advantages of Working with the polymers in an aqueous medium and at the same time avoiding the inherent disadvantages of water-sensitivity of the coatings or films deposited therefrom required dispersing the polymer as extremely small particles. The coatings or films deposited from such emulsions do exhibit a satisfactory waterresistance, but due to the fine particle size which imparts the water-resistance, the emulsions do not have the tack necessary to make them useful as quick-setting adhesives, i i

It is an object of this invention to provide a composition comprising an aqueous emulsion of a polymer, particularly a polymer of vinyl ace- We, alone r n c m inat n, with sma l uai tities of other monomers, which is stable through! out long periods of storage and which when em; ployed as a coating or as an adhesive will deposit a coating or bond which is highly waters resistant. A further object of the invention is to provide a process which is generally applicable to modify emulsions of polymers, particularly polyvinyl acetate, which have been polymerized di e nt extents or i fier t l t l t s v and which include various combinations of plasticizers and other diluents commonly employed to die-.- velop favored characteristics in the films or coatings deposited from such emulsions.

This procedure is obviously not We have discovered that the water-resistance of coatings or bonds deposited from an aqueous emulsion of polymers, particularly polyvinyl acetate emulsions, which are formulated, or modified, to have a tackiness rendering them suitable for use as quick-setting adhesives, can be established by additions of one or more of a certain group of organic compounds within specific limits. These active compounds are characterized by a particular balance between the parts of the molecule, one part of which is hydrophilic or polar in nature, and the other part of which is hydrophobic or non-polar. The effectiveness of the compounds in producing water-resistance in the coatings or bonds deposited from such emulsions is apparently due to the presence of both the polar and non-polar groups within the molecule in the prescribed balance.

As a class, these active compounds exhibit solubility, to various extents, in both water and in organic solvents such as mineral spirits, petroleum ether, toluene, castor oil, etc. This solubility in both water and organic solvents apparently is due to the dual hydrophilic-hydrophobic nature of the compound. As it has been generally recognized that the presence of watersoluble emulsifiers carried into the bonds and coatings deposited from emulsions of water-insoluble polymers may later cause redispersion and disintegration of the bonds and coatings, it was particularly surprising to find that incorporating into the emulsion additional compounds which are water-soluble themselves will nullify the efiect of the water-soluble emulsifiers and thereby impart water-resistance to the coatings and films deposited from such emulsions.

For present purposes a polar or hydrophilic group or radical may be considered to be one which has a strong aflinity for water and which when combined in compounds in which it is the dominant functional group will cause the resulting compound to be immiscible, or miscible to a limited extent, in oil-type solvents. A non-polar or hydrophobic group, on the other hand, may be considered to be one which has slight afiinity for water and a strong afiinity for oil-type solvents. The hydroxyl group, for example, has a strong polar character. Hydrocarbon chains may be considered as non-polar groups.

In some instances, it has been observed that the substitution of a strongly polar group, such as the hydroxyl group, by an acetate radical will sufliciently alter the polar character of a compound and, within defined limits, will result in establishing the requisite polar-non-polar balance within the previously inoperative polar compound.

For example, glycerol, having 3 carbon atoms and 3 hydroxyl groups is entirely too hydrophilic, but the esterified derivatives such as diacetin and triacetin were found to be very effective as the substitution of the acetate radical for one or more of the strongly polar hydroxyl groups established the requisite polar-non-polar balance in the molecule.

The preferred range of quantities of one or more of the active compounds by weight with respect to the solid content of the polyvinyl acetate emulsion has been found to be between about 8 to 25 percent, the optimum amount in a particular instance depending upon the initial waterresistancecharacteristics of the starting material emulsion, the amount of plasticizers employed, and the age of the starting material emulsion.

It will be understood, however, that compo 4 tions having up to 50% active compound by weight of solid content of the starting material emulsion can be employed, especially where the active compound exhibits desirable plasticizing properties and the cost thereof is not Drohibi-- tive.

The physical properties of a polyvinyl acetate emulsion such as the viscosity of the emulsion and the tensile strength, flexibility and heat sealing temperature of the film or bond deposited from the emulsion are determined in a large part by the degree of polymerization of the vinyl acetate monomer. A higher degree of polymerization results in increased bond strength, a higher heat sealing temperature and a somewhat higher initial water-resistance, which is. however, considerably less than required commercially for a water-resistant coating or bond. A lesser quantity of the active compounds is necessary to impart the desired water-resistance to the deposited coatings or bonds when the relatively greater water-resistant emulsions are employed as a starting material.

For present purposes the polyvinyl acetate starting material emulsions having sufiicient tack to be useful as quick-setting adhesives and suit able for improvement according to the instant invention may be classified according to their initial water-resistance although in each instance the water-resistance is negligible from the standpoint of minimum commercial requirements. Such emulsions generally contain about 40-65% polyvinyl acetate by weight, and a dried bond produced by the respective emulsions between two sheets of mildly calendered white sulphite paper will open up within 24 hours after immersion in water at about 25 C.

Such polyvinyl acetate emulsions include the commercially available emulsions known as Elvacet No. -900, Elvacet 81-900, Gelva S50, Polyco 11TH, Polyco l1'7-SS and Polyco 289.

The physical characteristics of the commercially available polyvinyl acetate emulsions identified above may also vary to some extent as a result of the emulsifiers and bodying agents employed in producing the emulsions, and also as a result of particular plasticizers employed. In general, however, the variations which tend to increase the relative initial Water-resistance of the starting material emulsions lessen the quantity of the active compounds required to afiect complete water-resistance.

The amounts of active compound required to produce maximum Water-resistance in a particular emulsion also varies with the quantity and the nature of the plasticizers, extenders, or other diluents which may be used to develop desired characteristics of fluidity or tackiness in the emulsion, or of flexibility, hardness, etc. in the coating or film deposited from the emulsion. In general, it has been found that the insoluble type of plasticizers and resins in common use increase the effectiveness of the active compounds, and that a lesser quantity of active compound is necessary to produce complete Water-resistance when such plasticizers are also present in the emulsion. It should be noted, however, that in each instance the emulsion containing the plasticizers and various other diluents was not initially water-resistant and that the addition of the active compound is necessary to afiect any satisfactory water-resistance, although as related above, a lesser amount is necessary when insoluble plasticizers are also present.

This enhancing effect of the insoluble plastiel ers was, particularly observed with respect: to dimethy-l phthalate, dibutyl phthalate, chlorinate eddiphenyls', methyl abietate and tributyl phos phate, and app ars to be characteristic of other common plasticizers such as di-carbitol phtha.-. late, dibutoxy-glycol phthalate, dimethoxy-glycol phthalate, butyl phthalyl butyl glycolate, methyl phthalyl ethyl glycolate, triglycol di-2- ethylbutyrate, triglycol di-Z-ethylhexoate, trires he h te and inhenyl phosp at n the other hand, the presence of a small amount of certain water-soluble thiclreners such aspolyvinyl alcohol and sodium carboxymethyl cellulose tend to increase the amount of active compound necessaryto effect maximum waterresistance.

In some instances care must be exercised to avoid breaking the emulsion by sudden heating, or by extended heating above the temperature specified, The critical temperature will vary, of course, with the character of the particular starting material emulsion employed.-

Aging the composition also tends to increase the water-resistance of the coatings or films deposited therefrom.

It will be apparent from the foregoing that innumerable possibilities for formulating the instant water-resistance composition exist, and that the invention may be practiced to increase the water-resistance of any particular polyvinyl acetate emulsion without materially interfering with the versatility of the starting material emulsion.

The addition of the active compound to the starting material emulsion may result in a substantial increase in the viscosity of the emulsion to form a cohesive mass unless the active com: pound is added slowly with continuous agitation. In some instances rapid addition of the active compound results in localized precipitation of the emulsion. The largest part of the increased cohesiveness and viscosity of the emulsion caused by addition of the active compound at a suitable rate disappears on agitation, or when the treated emulsion is permitted to stand for a short period following the addition of the active compound.

In all of the following examples the composi tion was prepared by stirring the starting material emulsion with a high-speed mixer continuously during the addition of the active compound thereto. Ihe active compound was introduced into the emulsion at the rate of about 3% of the total weight of the active compound per minute.

Preliminarily, each of the tacky starting material polyvinyl emulsions was applied as a coating on the surface of a moderately calendered and sized white sulphite paper and as a bond between two such papers. The films and bonds thus formed were allowed to dry for 24 hours at room temperature and were thereafter immersed in water at room temperature for 24 hours. Upon removal from the water the wet strength of the paper exceeded the bond strength in all cases, and the bond ruptured when the bonded papers were separated. The coatings in each instance had visibly disintegrated. These starting material emulsions were, therefore, considered nonwater-resistant, and in the subsequent experiments, satisfactory water-resistance of a film or bond formed from an emulsion treated with an active compound was considered fully indicated when the strength of the bond exceeded the wet strength of the paper after 24 hours immersion.

6 Enameled sample as prepared by ad ing 6 p rs o a m hyl abietate plastici er to 1.10 p ts of a t c y pol iny acetate e s on wh l he e s o a st rred t uqusl wi h a hi p ed m S ven addit on l sampl s were pr pared by intimately adm xin pa ts f a t ky po y vinyl acetate emulsion with 6 parts of a methyl chic-tats plasticizer an slowlyv a din theretowih. ccntinuo st rring l 1Q, 2, 5 a 18% diacetin, "respectively, by weight of the solid content at h starting ma ial emulsion.

All eight samp s we ested, fo r-r s an e b apply ng them. as b th a a bond to mildly calendered white sulphite paper. The films and bonds thus prepared were allowed to dry for 24 hours and thereafter immersed in water for an additiOnal 24 hours. At the end of this period it was found that the films and bonds deposited from the mixture of starting material emulsion and plasticizer, and from the samples containing, respectively, 5 and 7% diacetin by weight of the starting material emulsion had visibly disintegrated. The films were discontinuous and redispersion had occurred. The strength of the bonds did not exceed the wet strength of the paper and when the bonded papers were separated the bonds were fractured. The films and bonds deposited from the samples containing 8% or more of diacetin were waterresistant. The films were continuous and intact. The bond strength exceeded the wet strength of the paper and when the bonded papers were separated the surface of the papers was torn. The bonds remained intact.

Example 2 Eight samples were prepared in'the manner described in Example 1 using the same amount of starting material emulsion, plasticizer and diacetin, were used, except that a dibutyl phthalate plasticizer was employed in place of the methyl abietate used in the samples of Example l.

All the samples were tested for water-resistance in the manner specified in Example 1. The films and bonds deposited from the samples containing 7% and less of diacetin by weight of the solid content of the starting material emulsion had visibly disintegrated as a result of the 24 hour immersion in water. The wet strength of the paper exceeded the bond strength and the bonds fractured when the bonded papers were separated. The films and bonds deposited from the samples containing 8% or more of diacetin were water-resistant. At the end of the period of immersion the films were continuous and intact and the bond strength exceeded the wet strength of the paper.

A portion of each of the waterproof samples stood for a period of six months. At the end of this time the appearance and feel of the sample was unchanged. No hydrolysis, settling or discoloration was observed.

It will be apparent that the water-resistant compositions formulated according to the instant invention will considerably extend the usefulness of aqueous emulsions of polyvinyl acetate into the field in which high water-resistance of the bond or coating deposited is necessary, and will find application in bonding or cementing for cellulosic articles such as paper cups or paper bags which in the course of normal use are exposed to water, and for bonding surfaces or cellulosic material to other surfaces of a hydrophilic character such as masonry. These instant compositions are particularly adapted for use as a sizing where water-resistance of the fabric or the paper to which it is applied is required. It may also be employed in the composition of printing paste, as a finish for paper, paper-board, or foils and in the manufacture of formed or impregnated goods, as well as distemper aints and the like.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A composition consisting of a tacky aqueous emulsion of polyvinyl acetate, a plasticizer for said acetate and from 4 to 50% by weight of said acetate of an acetic acid ester of glycerol.

2. A composition consisting of a tacky aqueous emulsion of polyvinyl acetate and from 4 to 50% by weight of said acetate of di-ace-tin.

3. A base having a coating deposited from a 20 composition consisting of a tacky aqueous emu1- sion of polyvinyl acetate and from 4 to'50% by weight of said acetate of an acetic acid ester of glycerol.

8 4. A base having a coating deposited from a composition consisting of a tacky aqueous emulsion of polyvinyl acetate, a plasticizer for said acetate, and 450% by weight of said acetate of diacetin.

WALTER G. KUNZE.

R. BERTRAM EVANS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,025,044 Dreyfus Dec. 24, 1935 2,105,952 Moss Jan. 18, 1938 2,435,909 Tompkins Feb. 10, 1948 2,444,396 Collins et al. June 29, 1948 FOREIGN PATENTS Number Country Date 518,704 Great Britain Mar. 5, 1940 

1. A COMPOSITION CONSISTING OF A TACKY AQUEOUS EMULSIONI OF POLYVINYL ACETATE, A PLASTICIZER FOR SAID ACETATE AND FROM 4 TO 50% BY WEIGHT OF SAID ACETATE OF AN ACETIC ACID ESTER OF GLYCEROL. 